1. Field of the Invention
The present invention relates to an information processing method for erasing information recorded on an erasable recording medium and to an apparatus therefor.
2. Related Background Art
A magneto-optical recording medium 52 whose cross-section is schematically shown, for example, in FIG. 1A of the accompanying drawings is known as an erasable recording medium. This magneto-optical recording medium has as a recording layer 53 of a magnetic film whose readily magnetizable axis is perpendicular to the film surface. Recording of information may be accomplished by arranging the directions of magnetization of the recording layer 53 in a first direction in advance, and scanning the recording layer by a light beam 54 intensity-modulated in conformity with the information while extraneously applying a magnetic field M.sub.R in the direction opposite to the first direction. The portion of the recording layer to which the light beam is applied is once demagnetized, thereby, and is subsequently magnetized in a direction to opposite to the first direction by an extraneous magnetic field and forms a recording bit 55 corresponding to the information as shown in FIG. 1B of the accompanying drawings. The thus recorded information may be read out in a well-known manner using the magneto-optical effect by applying an unmodulated light beam of low intensity to the recording layer and detecting the light reflected by or transmitted through the recording layer. When the recorded information is to be erased, a light beam 56 is applied to the area in which the information is recorded while an extraneous magnetic field M.sub.E in the direction opposite to the direction of magnetic field M.sub.R (i.e., the direction in which the recording layer was magnetized before recording) is applied to the recording layer as shown in FIG. 1C of the accompanying drawings.
To accomplish reliable erasing without leaving any unerased portion when the information is to be erased as described above, it is necessary that the erasing light beam accurately scan the area in which the information is recorded. So, in U.S. Pat. No. 4,953,150 (same assignee) it is proposed to, increase the power of the light beam during erasing from that used in recording. This is a technique for reliably accomplishing erasing even if more or less deviation of the scanning region is caused in a direction perpendicular to the direction in which the recording bit row continues (the so-called tracking direction) by making the erasing range by the light beam larger than the width of the recording bit. However, although the error in the tracking direction is allowable in the above-described technique, such a technique has still been insufficient when the error in the beam scanning direction is taken into consideration. This will be described hereinafter.
As shown in the schematic plan view of FIG. 2A of the accompanying drawings, a magneto-optical recording medium is generally divided into predetermined units called sectors. Each sector, in turn, is divided into an address area and a recording area, and a gap portion is provided therebetween. In the address area, an address number, or the like, indicative of the position of that sector on the medium is pre-recorded by an unerasable bit 58 formed by the unevenness, or the like, of the medium substrate. In the recording area, the recording bit 57 is magnetically recorded by the aforedescribed method. Also, this sector is separated from the next sector by a sector gap.
Here, when the recording bit 57 is to be erased, the recording area may be scanned by an erasing light beam spot 59 as shown in FIG. 2B. However, if the light beam is turned-on too late or turned-off too early due to the error of the timing count for turning on and turning off the light beam and due to the irregularity of the beam scanning speed, unerased portions 60 of the recording bit are caused as shown in FIG. 2C of the accompanying drawings. Such unerased portions 60 have caused a reduction in the reliability of recording when information is re-recorded in this area.